1. Field of the Invention
The present invention relates to an illumination control circuit used in an on-vehicle apparatus such as a car stereo system having an optical remote control feature which enables functions of the stereo system such as loudness control, tuner/CD selection, and FM/AM selection to be carried out by remote control.
2. Related Art
Conventional on-vehicle apparatuses such as car stereo systems are usually provided with illuminated push buttons, switches, and displays for improved operability and improved attractive appearance.
FIG. 11 shows an illumination control circuit used in conventional car stereo systems. In the figure, a dimmer signal, usually supplied from the vehicle for illuminating an instrument panel of the vehicle, is used as an illumination control signal for the on-vehicle apparatus. The dimmer signal controls an illumination switch 2 of a car stereo system 1 to become on or off so as to effect illumination of the various controls on the panel of the car stereo system 1. With the conventional circuit in FIG. 11, the on and off control of illumination lamp 3 is drivingly effected by the actuation of the illumination of vehicle instruments. Thus, a cord or cable needs to be connected between the dimmer switch of the vehicle and the car stereo system 1. This assembly of the cable requires additional assembly steps. Further, the cable may pick up external noises and therefore a noise filter 4 is needed as shown.
FIG. 12 shows another example of an illumination control circuit where a built-in photoreceptor 5 is used instead of the dimmer signal in FIG. 11 to control the brightness of illumination lamp 3. The photoreceptor 5 is disposed at an appropriate position on the operating panel of car stereo system 1 so as to detect the visible lights in the passenger space of vehicle. The output of photoreceptor 5 drives a current control section 6 so as to controllably vary the brightness of illumination lamp 3 in accordance with the visible light in the passenger space.
With the conventional circuit in FIG. 12, the photoreceptor 5 must be arranged together with push buttons and switches on the operating panel of car stereo system 1. Miniaturization is of prime importance in on-vehicle apparatuses such as car stereo systems because an available panel area is particularly limited as to space for buttons, etc. The photoreceptor 5 does take up a finite mounting space, placing a limitation on the ability to achieve increased miniaturization of apparatus as well as the resulting in adverse effects in arranging push buttons and switches on the operating panel.